Field of Invention
The present invention relates to a micro-electro-mechanical system (MEMS) device, especially an MEMS device including an internal anchor area and a multi-dimensional spring.
Description of Related Art
MEMS devices have become common in our daily life; one typical function of the MEMS devices is for motion sensing. FIG. 1 shows a prior art MEMS device 10 disclosed in U.S. Pat. No. 6,892,576, wherein only one fourth of the MEMS device 10 is shown and the rest three fourths are symmetrical. A proof mass 11 is connected to a substrate (not shown) through multiple springs 12, multiple linkages 13, and multiple anchors 15. Sensing electrodes are connected to the substrate through multiple anchors 14. In this prior art, the linkage 13 requires anchors 15 so that it can be connected to the substrate without distortion, and the center of the proof mass 11 as well as the anchors 15 need to be close to a multiple anchors 14. Under these limitations, the layout and manufacturing process of the structure are quite complicated.
FIG. 2 shows another prior art MEMS device 20 disclosed in U.S. Pat. No. 8,333,113, wherein three springs 21, 22, and 23 (with different moving directions) are respectively connected to different proof masses. The MEMS device 20 includes an anchor 24 which is connected to the substrate 25. In this prior art, each spring and each proof mass requires an individual structure. Thus, the merit of single proof mass for 3-axis sensing may not be accomplished easily.
FIG. 3 shows another prior art MEMS device 30 disclosed in U.S. Pat. No. 8,610,222, which includes proof masses 31 and a fixing part 32 (both shown by the white regions), wherein the outer proof mass 31 is connected to the inner proof mass 31 through multiple springs 37, and the inner proof mass 31 and the fixing part 32 are connected as one part. For avoiding a short circuit between the proof mass 31 and the fixing part 32, an insulation structure 38 is provided between the inner proof mass 31 and the fixing part 32. The proof mass 31 is connected to the substrate 35 through anchors 34, and the fixing part 32 is connected to the substrate 35 through the anchors 33. In this prior art, the layout of the anchors is so arranged that the anchors 33, 34, and 36 are located near a central area of the proof mass 31, so as to minimize the offset due to deformation. However, the insulation structure between the proof mass 31 and the fixing part 32 substantially increases the manufacturing complexity and reduces the strength of the structure. Generally, the proof masses, the fixing part, and the springs are made of same material, and the sacrificial layers surrounding these parts are made of an insulating material such as an oxide. The proof masses and the springs are released by etching the insulating material. Therefore, if an insulation structure needs to remain in the final MEMS device, this will greatly increase the complexity of the manufacturing process. Besides, the reliability issue of the product must be taken care of.
In view of the drawbacks of the prior art MEMS devices, the present invention provides an MEMS device having an anchor layout capable of minimizing the offset due to deformation, without the need of complicated process to manufacture.